Synthesis of 4,4′-bipyridinium salts of poly(2-methoxyaniline-5-sulfonic acid) and their self-doping and chemical properties

4,4′-Bipyridinium salts (PAS-BPy(R)s) of poly(2-methoxyaniline-5-sulfonic acid) (PAS) were synthesized by the reaction of PAS with N-4-halophenyl-4-(4-pyridyl)pyridinium chlorides (BPy(X)s) or N-2,4-dinitrophenyl-4-(4-pyridyl)pyridinium chloride (BPy(NO2)). The UV-vis, ESR and X-ray photoelectron spectroscopy (XPS) data suggested the occurrence of the self-doping in PAS-BPy(R)s that was based on the electron transfer from the nitrogen atom in the polymer backbone to the 4,4′-bipyridinium unit. PAS-BPy(R)s behaved as polymeric electrolytes in the dilute solutions. Electric conductivity of PAS-BPy(R)s was almost constant when it was measured in the range of 1 ⩽ pH ⩽ 10. Cyclic voltammetry suggested that PAS-BPy(R)s received two-step electrochemical reduction in film, and the electrochemical reaction was accompanied with electrochromism.